The invention relates to a system for controlling a chassis, in particular for controlling spring cylinders that can perform the function of a semiactive shock absorber at the same time and that are disposed between wheel suspensions and the vehicle body.
Especially in automotive engineering, the development of electronic chassis control systems is directed to purposefully adapting the damping characteristic to the particular driving status of the vehicle. Oriented damper adjustment, for example, by means of valves that are adjustable as a function of control signals is done as a function of sensor signals, which detect various parameters of the driving status (such as vehicle speed, vehicle inclination, transverse and vertical acceleration, and up-and-down, pitching and rolling motions). Moreover, in the low-frequency range of vehicle body motions, active interventions should be made, to react to pitching, up-and-down, and rolling motion.
In these control signals, a distinction is made between so-called passive and active control signals. Passive control signals are directed to a slowly adaptive adjustment of the damping as a function, for instance, of driving performance desired by the driver, road conditions, or the vehicle speed.
Active control signals, contrarily, are meant to exert direct influence on the applicable absolute speed of the vehicle body (raising, lowering, pitching, rolling) within the shortest possible periods of time. The entire damper system may be designed such that the passive damping control increases or decreases the damping action in the same direction with respect to tension and compression, while the active damping control makes the damping asymmetrical as a function of external signals, or in other words varies the damping action in opposite directions in the compression and tension stages. The overall result is a so-called semiactive damper system.
A system for controlling shock absorbers is disclosed for instance in German Patent No. 16 30 058. There, two work chambers of a shock absorber or spring strut are connected via external lines to an apparatus that comprises a pump and two reservoirs. Only single-action check valves are provided as valves in the connecting lines to the spring strut. With such an apparatus, however, the damper hardness of a shock absorber cannot be varied, because energy would have to be supplied from outside via the pump for that purpose, which takes a relatively long time and uses a certain amount of power.
German published patent application no. 33 04 815 also shows a way of controlling shock absorbers in which optimization is directed to a middle operating situation in terms of spring hardness and damper hardness; the corresponding parts and their parameters are structurally designed with a view to this. These parameters then remain unchanged during vehicle operation. As a result, however, extreme operating situations, such as an empty vehicle or a fully loaded vehicle in particular, or changing vehicle operating parameters (cornering, braking, acceleration, comfortable superhighway travel, or the like), go undetected.
In U.S. Pat. No. 3,807,678, active intervention is also made into the positive displacement of pressure fluid volume in the shock absorber. To this end, the two work chambers of a shock absorber are each connected crosswise and parallel to one another via oppositely directed valves that allow a flow of pressure fluid solely in one direction; the quantity of pressure fluid admitted by these valves is then furthermore determined "actively" by corresponding triggering of the valves with suitably prepared sensor signals. The externally located spring remains entirely passive, so that the entire system is one of semiactive control.
The above-described semiactive damper control is not adequate for optimal calming of vehicle body motion. That requires a partly active chassis control system, which supplies active energy to the spring cylinder or removes such energy from it.